The Return of the Horny Dead by Rhonda Lee

During a terrible blizzard Steffie finds a naked man with a Y incision on his chest standing in the middle of her garage. Thinking he's wandered away from the hospital and is suffering from hypothermia, Steffie brings him into her house and attempts to warm him up. Things get hot alright as Steffie gives her visitor the sexy show of his (un)life and gets a little more than she bargained for in the process.

There was a naked man standing in the middle of my garage. His back was to me, but he was very definitely a man, and a well hung one at that-his legs were slightly apart and I could see his cock dangling down between them. He was buff too, but pale, sort of grey-ish actually, I figured that was hardly surprising since he was standing in my garage nude in the middle of the worst snowstorm in recent memory.

Now, I'm no idiot-I considered the fact that he could very well be crazy, and I did consider just turning around and walking back to my house-but my conscience got the better of me. If he wasn't dangerous I couldn't very well just leave him there to freeze to death could I? I figured I had to take the chance, or else I'd never be able to look at myself in the mirror again-and I am rather fond of looking at myself in the mirror.

I cleared my throat to get his attention, which is when I realized that my garage was better insulated than I thought, because even over the howling of the wind, he seemed to have heard me in here. He stiffened up, every muscle in his body seemed to suddenly come alert and his head, which had been hanging down as though he were looking at the floor, suddenly jerked up.